U.S. patent number 6,002,208 [Application Number 09/109,684] was granted by the patent office on 1999-12-14 for universal cold-cathode type ion source with closed-loop electron drifting and adjustable ion-emitting slit.
This patent grant is currently assigned to Advanced Ion Technology, Inc.. Invention is credited to Yuri Maishev, James Ritter, Leonid Velikov.
United States Patent |
6,002,208 |
Maishev , et al. |
December 14, 1999 |
Universal cold-cathode type ion source with closed-loop electron
drifting and adjustable ion-emitting slit
Abstract
A universal cold-cathode type ion source with a closed-loop
electron drifting source and with an ion-beam propagation direction
perpendicular to the plane of electron drifting is intended for
uniformly treating stationary or moveable objects with such
processes as cleaning, activation, polishing, thin-film coating, or
etching. The ion source of the invention allows adjustment of beam
parameters and configurations and has an ion emitting slit of an
adjustable geometry. In one embodiment, the adjustment is carried
out by changing the width of the slit by shifting moveable parts of
the cathode in the direction perpendicular to the direction of the
ion beam. In another embodiment the slit configuration is adjusted
by shifting a moveable part of the cathode in the direction of the
beam propagation. The invention also provides a method for
adjusting the shape and configuration of the ion beam with respect
to the object to be treated. The adjustment can be performed during
the operation of the ion beam while observing the beam through a
sealed transparent window of the vacuum chamber.
Inventors: |
Maishev; Yuri (Moscow,
RU), Ritter; James (Fremont, CA), Velikov;
Leonid (San Carlos, CA) |
Assignee: |
Advanced Ion Technology, Inc.
(Fremont, CA)
|
Family
ID: |
22328981 |
Appl.
No.: |
09/109,684 |
Filed: |
July 2, 1998 |
Current U.S.
Class: |
315/111.91;
250/423R; 250/492.23; 315/111.41 |
Current CPC
Class: |
H01J
27/143 (20130101) |
Current International
Class: |
H01J
27/04 (20060101); H01J 27/02 (20060101); H01J
027/02 () |
Field of
Search: |
;315/111.31,111.41,111.81,111.91 ;250/492.23,423R |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
Re30171 |
December 1979 |
Kruger et al. |
4122347 |
October 1978 |
Kovlasky et al. |
4710283 |
December 1987 |
Singh et al. |
5350920 |
September 1994 |
Fukuyama et al. |
|
Foreign Patent Documents
Primary Examiner: Bettendorf; Justin P.
Attorney, Agent or Firm: Zborovsky; Ilya
Claims
What we claim is:
1. A universal ion beam source with a closed-loop ion-emitting slit
capable of emitting an ion beam toward an object located in a
position reachable by said ion beam, comprising:
a hollow housing that functions as a cathode of said ion beam
source;
an anode located in said hollow housing and spaced from said
cathode to form an ionization gap therebetween for ionization and
acceleration of ions formed in said gap during operation of said
ion beam source,
magnetic field generating means in magnetoconductive relationship
with said anode and said cathode for forming closed
magnetoconductive circuit passing through said anode, said
ionization gap, said cathode, and said magnetic field generating
means;
a closed-loop ion emitting slit formed in said cathode in the path
of said magnetoconductive circuit, said closed-loop ion emitting
slit having predetermined geometric dimensions defined by an inner
profile and an outer profile;
electric power supply means for maintaining said anode under a
positive charge and said cathode under a negative charge with
respect to said anode;
means for the supply of a working medium into said hollow housing
of said cathode to form an ion beam when said working medium passes
through said ionization gap, said beam having a direction of
propagation towards said object; and
means for adjusting said predetermined geometric dimensions of said
closed-loop ion emitting slit and thus for adjusting performance
characteristics of said ion beam source,
said cathode having a stationary part and a moveable part, said
means for adjusting said predetermined geometric dimensions of said
closed-loop ion emitting slit comprising means for moving said
moveable part of said cathode with respect to said stationary part
of said cathode.
2. The ion beam source of claim 1, wherein one of said
predetermined geometric dimensions is the width of said closed-loop
ion emitting slit and wherein said moveable part of said cathode
defines said width and is moveable in the direction perpendicular
to said direction of propagation of said ion beam.
3. The ion beam source of claim 2, wherein said moveable part of
said cathode consists of two members that define two opposite sides
of said closed-loop ion emitting slit and that are moveable
simultaneously and in mutually opposite directions.
4. The ion beam source of claim 3, wherein said magnetic field
generating means is at least one permanent magnet.
5. The ion beam source of claim 4, wherein said closed-loop ion
emitting slit has a shape selected from a group consisting of
rectangular, circular, oval, and elliptic shapes.
6. The ion beam source of claim 1, wherein said means for adjusting
has a first part connected to said moveable pan of said cathode and
a second part that extends outside said hollow housing through
sealing means for controlling movements of said moveable part of
said cathode from outside of said universal ion beam source.
7. The ion beam source of claim 1, wherein said means for adjusting
is at least one screw having a round head freely rotating in a
recess formed in said moveable part of said cathode and a threaded
portion engageable with a threaded opening in a part stationary
with respect to said moveable part of said cathode.
8. The ion beam source of claim 1, wherein said hollow housing has
guides for guiding said moveable part in said direction of
propagation of said beam towards said object.
9. The ion beam source of claim 8, wherein said moveable part of
said cathode is a central part of said cathode which defines said
inner profile of said ion-emitting slit.
10. The ion beam source of claim 9, wherein said magnetic field
generating means is at least one permanent magnet.
11. The ion beam source of claim 10, wherein said closed-loop ion
emitting slit has a shape selected from a group consisting of
rectangular, circular, oval, and elliptic shapes.
12. The ion beam source of claim 11, wherein said magnetic field
generating means is connected to said moveable part of said cathode
for moving integrally therewith.
13. The ion beam source of claim 12, wherein said means for
adjusting has a first part connected to said moveable part of said
cathode and a second part that extends outside said hollow housing
through sealing means for controlling movements of said moveable
part of said cathode from outside of said universal ion beam
source.
14. The ion beam source of claim 13, wherein said hollow housing
has a guide portion, said guide portion containing a guide member
which is connected to said permanent magnet, and said means for
adjusting being made in the form of at least one screw having a
round head freely rotating in a recess formed in said second part
and a threaded portion engageable with a threaded opening in a part
stationary with respect to said moveable part.
15. A method for adjusting performance characteristics of an ion
beam source with a closed-loop ion emitting slit of predetermined
geometric dimensions, comprising the steps of:
providing said ion-beam source with means for adjusting said
predetermined geometric dimensions of said closed-loop ion emitting
slit; and
adjusting performance characteristics of said ion beam by changing
said predetermined geometric dimensions of said closed-loop ion
emitting slit, said step of adjustment being performed by adjusting
the width of said closed-loop ion emitting slit, said ion beam
source having a cathode comprising a stationary part and a moveable
part, said adjustment being performed by moving said moveable part
of said cathode in the direction perpendicular to the direction of
propagation of said ion beam.
16. A method for adjusting performance characteristics of an ion
beam source with a closed-loop ion emitting slit of predetermined
geometric dimensions, comprising the steps of:
providing said ion-beam source with means For adjusting said
predetermined geometric dimensions of said closed-loop ion emitting
slit; and
adjusting performance characteristics of said ion beam by changing
said predetermined geometric dimensions of said closed-loop ion
emitting slit, said step of adjustment being performed by adjusting
the width of said closed-loop ion emitting slit, said ion beam
source having a cathode comprising a stationary part and a moveable
part, said adjustment is performed by moving said moveable part of
said cathode in the direction of propagation of said ion beam.
17. A method for adjusting performance characteristics of ion beam
source with a closed-loop ion emitting slit of predetermined
geometric dimensions, comprising the steps of:
providing said ion-beam source with means for adjusting said
predetermined geometric dimensions of said closed-loop ion emitting
slit;
generating an ion beam by means of said ion beam source;
directing said ion beam onto the surface of an object to be
treated;
observing the shape of said ion beam and its location with respect
to said surface of said object; and
adjusting performance characteristics of said ion beam by changing
said predetermined geometric dimensions of said closed-loop ion
emitting slit while observing said shape and location of said ion
beam, said step of adjustment being performed by adjusting the
width of said closed-loop ion emitting slit; said ion beam source
having a cathode comprising a stationary part and a moveable
part, said adjustment being performed by moving said moveable part
of said cathode in the direction perpendicular to the direction of
propagation of said ion beam.
18. A method for adjusting performance characteristics of ion beam
source with a closed-loop ion emitting slit of predetermined
geometric dimensions, comprising the steps of:
providing said ion-beam source with means for adjusting said
predetermined geometric dimensions of said closed-loop ion emitting
slit;
generating an ion beam by means of said ion beam source;
directing said ion beam onto the surface of an object to be
treated;
observing the shape of said ion beam and its location with respect
to said surface of said object; and
adjusting performance characteristics of said ion beam by changing
said predetermined geometric dimensions of said closed-loop ion
emitting slit while observing said shape and location of said ion
beam, said step of adjustment being performed by adjusting the
width of said closed-loop ion emitting slit, said ion beam source
having a cathode comprising a stationary part and a moveable
part, said adjustment being performed by moving said moveable part
of said cathode in the direction of propagation of said ion beam.
Description
FIELD OF THE INVENTION
The present invention relates to ion-emission technique,
particularly to cold-cathode ion sources used for cleaning,
activation, polishing, or thin-film coating of surfaces. More
specifically, the invention relates to a universal cold-cathode
type ion source with ion-beam propagation direction perpendicular
to the plane of electron drifting. The source is intended for
treating objects of different configurations and with large surface
areas.
BACKGROUND OF THE INVENTION AND DESCRIPTION OF THE PRIOR ART
An ion source is a device that ionizes gas molecules and then
focuses, accelerates, and emits them as a narrow beam. This beam is
then used for various technical and technological purposes such as
cleaning, activation, polishing, thin-film coating, or etching.
An example of an ion source is the so-called Kaufman ion source,
also known as a Kaufman ion engine or an electron-bombardment ion
source described by Kaufman H. R. in: An ion Rocket with an
Electron-Bombardment Ion Source, NASA Technical Note, TND-585,
January 1961.
This ion source consists of a discharge chamber in which a plasma
is formed, and an ion-optical system which generates and
accelerates an ion beam to an appropriate level of energy. A
working medium is supplied to the discharge chamber which contains
a hot cathode that functions as a source of electrons and is used
for firing and maintaining a gas discharge. The plasma, which is
formed in the discharge chamber, acts as an emitter of ions and
creates, in the vicinity of the ion-optical system, an ion-emitting
surface. As a result, the ion-optical system extracts ions from the
aforementioned ion-emitting surface, accelerates them to a required
energy level, and forms an ion beam of a required configuration.
Typically, aforementioned ion sources utilize two-grid or
three-grid ion-optical systems. A disadvantage of such a device is
that it is not suitable for treating large surfaces. Another
disadvantage is that the ion beam has low intensity.
Attempts have been made to provide ion sources with ion beams of
higher intensity by holding the electrons in a closed space between
a cathode and an anode where the electrons could be held. For
example, U.S. Pat. No. 4,122,347 issued in 1978 to Kovalsky et al.
describes an ion source with a closed-loop of electrons for
ion-beam etching and deposition of thin films, wherein the ions are
taken from the boundaries of a plasma formed in a gas-discharge
chamber with a hot cathode. The ion beam is intensified by a flow
of electrons which is held in crossed electrical and magnetic
fields within the accelerating space and which compensates for the
positive spatial charge of the ion beam.
A disadvantage of the devices of such type is that it does not
allow formation of ion beams of chemically-active substances for
ion beams capable of treating large surface areas. Other
disadvantages of the aforementioned device are short service life
and high non-uniformity of ion beams.
U.S. Pat. No. 4,710,283 issued in 1997 to Singh et al. describes a
cold-cathode type ion source with crossed electric and magnetic
fields for ionization of a working substance wherein entrapment of
electrons and generation of the ion beam are performed with the use
of a grid-like electrode. This source is advantageous in that it
forms belt-like and tubular ion beams emitted in one or two
opposite directions.
However, the ion source with a grid-like electrode of the type
disclosed in U.S. Pat. No. 4,710,283 has a number of disadvantages
consisting in that the grid-like electrode makes it difficult to
produce an extended ion beam and in that the ion beam is
additionally contaminated as a result of sputtering of the material
from the surface of the grid-like electrode. Furthermore, with the
lapse of time the grid-like electrode is deformed whereby the
service life of the ion source as a whole is shortened.
Other publications (e.g., Kaufman H. R. et al. (End Hall Ion
Source, J. Vac. Sci. Technol., Vol. 5, July/August, 1987, pp.
2081-2084; Wykoff C. A. et al., 50-cm Linear Gridless Source,
Eighth International Vacuum Web Coating Conference, Nov. 6-8,
1994)) disclose an ion source that forms conical or belt-like ion
beams in crossed electrical and magnetic fields. The device
consists of a cathode, a hollow anode with a conical opening, a
system for the supply of a working gas, a magnetic system, a source
of electric supply, and a source of electrons with a hot cathode. A
disadvantage of this device is that it requires the use of a source
of electrons with a hot or hollow cathode and that it has electrons
of low energy level in the zone of ionization of the working
substance. These features create limitations for using
chemically-active working substances. Furthermore, a ratio of the
emission slit width to a cathode-anode distance is significantly
greater than 1, and this decreases the energy of electrons in the
charge gap, and hence, hinders ionization of the working substance.
Configuration of the electrodes used in the ion beam of such
sources leads to a significant divergence of the ion beam. As a
result, the electron beam cannot be delivered to a distant object
and is to a greater degree subject to contamination with the
material of the electrode. In other words, the device described in
the aforementioned literature is extremely limited in its capacity
to create an extended uniform belt-like ion beam. For example, at a
distance of 36 cm from the point of emission, the beam uniformity
did not exceed .+-.7%.
Russian Patent No. 2,030,807 issued in 1995 to M. Parfenyonok, et
al. describes an ion source that comprises a magnetoconductive
housing used as a cathode having an ion-emitting slit, an anode
arranged in the housing symmetrically with respect to the emitting
slit, a magnetomotance source, a working gas supply system, and a
source of electric power supply.
FIGS. 1 and 2 schematically illustrate the aforementioned known ion
source with a circular ion-beam emission slit. More specifically,
FIG. 1 is a sectional side view of an ion-beam source with a
circular ion-beam emission slit, and FIG. 2 is a sectional plan
view along line II--II of FIG. 1.
The ion source of FIGS. 1 and 2 has a hollow cylindrical housing 40
made of a magnetoconductive material such as Armco steel (a type of
a mild steel), which is used as a cathode. Cathode 40 has a
cylindrical side wall 42, a closed flat bottom 44 and a flat top
side 46 with a circular ion emitting slit 52 having dimensions
defined by its inner profile 52a and an outer profile 52b.
A working gas supply hole 53 is formed in flat bottom 44. Flat top
side 46 functions as an accelerating electrode. Placed inside the
interior of hollow cylindrical housing 40 between bottom 44 and top
side 46 is a magnetic system which includes a cylindrical or oval
permanent magnet 66 with poles N and S of opposite polarity. An
N-pole faces flat top side 46 and S-pole faces bottom side 44 of
the ion source. The purpose of the magnetic system with a closed
magnetic circuit formed by parts 66, 40, 42, and 44 is to induce a
magnetic field in ion emission slit 52. It is understood that this
magnetic system is shown only as an example and that it can be
formed in a manner described, e.g., in aforementioned U.S. Pat. No.
4,122,347. A circular annular-shaped anode 54 which is connected to
a positive pole 56a of an electric power source 56 is arranged in
the interior of housing 40 around magnet 66 and concentric thereto.
Anode 54 is fixed inside housing 40 by means of a ring 48 made of
non-magnetic dielectric material such as ceramic. Anode 54 has a
central opening 55 in which aforementioned permanent magnet 66 is
installed with a gap between the outer surface of the magnet and
the inner wall of opening 55. A negative pole 56b of electric power
source is connected to housing 40 which is grounded at GR.
Located above housing 40 of the ion source of FIGS. 1 and 2 is a
sealed vacuum chamber 57 which has an evacuation port 59 connected
to a source of vacuum (not shown). An object OB to be treated is
supported within chamber 57 above ion emitting slit 52, e.g., by
gluing it to an insulator block 61 rigidly attached to the housing
of vacuum chamber 57 by a bolt 63 but so that object OB remains
electrically and magnetically isolated from the housing of vacuum
chamber 57. However, object OB is electrically connected via a line
56c to negative pole 56b of power source 56. Since the interior of
housing 40 communicates with the interior of vacuum chamber 57, all
lines that electrically connect power source 56 with anode 54 and
object OB should pass into the interior of housing 40 and vacuum
chamber 57 via conventional commercially-produced electrical
feedthrough devices which allow electrical connections with parts
and mechanisms of sealed chambers without violation of their
sealing conditions. In FIG. 1, these feedthrough devices are shown
schematically and designated by reference numerals 40a and 57a.
Reference numeral 57b designates a seal for sealing connection of
vacuum chamber 57 to housing 40.
The known ion source of the type shown in FIGS. 1 and 2 is intended
for the formation of a unilaterally directed tubular ion beam. The
source of FIGS. 1 and 2 forms a tubular ion beam IB emitted in the
direction of arrow A and operates as follows.
Vacuum chamber 57 is evacuated, and a working gas is fed into the
interior of housing 40 of the ion source. A magnetic field is
generated by magnet 66 in the accelerating gap between anode 54 and
cathode 40, whereby electrons begin to drift in a closed path
within the crossed electrical and magnetic fields. A plasma 58 is
formed between anode 54 and cathode 40. When the working gas is
passed through the ionization gap, tubular ion beam IB, which is
propagated in the axial direction of the ion source shown by an
arrow A, is formed in the area of an emission slit 52 and in an
accelerating gap 52a between anode 54 and cathode 40.
The diameter of the tubular ion beam formed by means of such an ion
source may reach 500 mm and more.
The ion source of the type shown in FIG. 1 is not limited to a
cylindrical configuration and may have an elliptical or an
oval-shaped cross section as shown in FIG. 3. In this case the
respective parts, i.e., side walls of the cathode 40.sub.ov, a
magnet 66.sub.ov, and an anode 54.sub.ov will have an-oval shaped
cross-section shown in FIG. 3 and will form an oval-shaped
ion-emiting slit 52.sub.ov. In FIG. 3 the parts of the ion beam
source that correspond to similar parts of the previous embodiment
are designated by the same reference numerals with an addition of
subscript OV. Structurally, this ion source is the same as the one
shown in FIG. 1 with the exception that a cathode 40.sub.ov, anode
54.sub.ov, a magnet 66.sub.ov and hence an emitting slit (not shown
in FIG. 3), have an oval-shaped configuration. As a result, a
belt-like ion beam having a width of up to 1400 mm can be formed.
Such an ion beam source is suitable for treating large-surface
objects when these objects are passed over ion beam IB emitted
through emitting slit 52.
With 1 to 3 kV voltage on the anode and various working gases, this
source makes it possible to obtain ion beams with currents of 0.5
to 1 A. In this case, an average ion energy is within 400 to 1500
eV, and a nonuniformity of treatment over the entire width of a
1400 mm-wide object does not exceed .+-.5%.
Nevertheless, the aforementioned belt-type ion source has limited
dimensions and is unsuitable for uniformly treating stationary
objects of large surface areas. Furthermore, it does not allow
simultaneous treatment of an object from different sides with a
plurality of beams controlled simultaneously or individually. It
cannot form extended ion beams of different configurations, such as
converging or diverging ion beams, nor can it form several ion
beams at the same time, and does not allow adjustment of ion beams
to form beams of different configurations.
OBJECTS OF THE INVENTION
It is an object of the invention to provide an ion source with a
closed-loop configuration of the ion emitting slit which allows
adjustment of geometrical dimensions of the ion emitting slit.
Another object is to provide an ion source of the aforementioned
type which may produce ion beams of different configurations.
Another object of the invention is to provide an ion source of the
aforementioned type which allows treatment of objects with
different surface areas.
Another object is to provide an ion beam source of the
aforementioned type which allows adjustment of an average energy of
ions in the beam.
Another object is to provide an ion beam source of the
aforementioned type which allows adjustment of the composition of
the ion beam, in case of a multiple-component gas used as a working
medium.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional side view of a known ion-beam source with a
circular ion-beam emission slit;
FIG. 2 is a sectional plan view along line II--II of FIG. 1.
FIG. 3 is a sectional plan view similar to the one of FIG. 2, but
with an oval-shaped sectional configuration of the ion-emitting
slit.
FIG. 4 is a sectional side view along the line IV--IV of FIG. 5
illustrating an ion-beam source according to an embodiment of the
invention with an emitting-slit width adjustable by shifting
moveable parts of the cathode in the direction perpendicular to the
direction of the ion beam.
FIG. 4a is a zone D of FIG. 4 shown on a larger scale.
FIG. 5 is a sectional view along line V--V of FIG. 4.
FIG. 6 is a sectional side view of an ion-beam source according to
another embodiment of the invention with an emitting slit
configuration adjustable by shifting a moveable part of the cathode
in the direction of the beam propagation.
FIG. 6A shows the position of moveable portion of the adjustable
cathode which provides the converging shape of the ion beam.
FIG. 6B shows the position of moveable portion of the adjustable
cathode which provides the diverging shape of the ion beam.
SUMMARY OF THE INVENTION
A universal cold-cathode type ion source with closed-loop electron
drifting and with ion-beam propagation direction perpendicular to
the plane of electron drifting is intended for uniformly treating
stationary or moveable objects with such processes as cleaning,
activation, polishing, thin-film coating, or etching. The ion
source of the invention allows for adjusting beam parameters and
configurations and has an ion emitting slit of an adjustable
geometry. In one embodiment, the adjustment is carried out by
changing the width of the slit by shifting moveable parts of the
cathode in the direction perpendicular to the direction of the ion
beam. In another embodiment the slit configuration is adjusted by
shifting a moveable part of the cathode in the direction of the
beam propagation.
DETAILED DESCRIPTION OF THE INVENTION
FIGS. 4, 4A, and 5--Ion Source with Adjustable Width of the
Emitting Slit
FIG. 4 is a sectional side view along the line IV--IV of FIG. 5
illustrating an ion-beam source according to one embodiment of the
invention in which the width of an ion-emitting-slit is adjustable
by shifting moveable parts of the cathode of the source in the
direction perpendicular to the direction of the ion beam emitted by
the source. FIG. 5 is a sectional view along line V--V of FIG.
4.
To some extent, an ion-beam source 100 of this embodiment is
similar to the known ion source with a circular ion-beam emission
slit of the type shown and described in connection with FIGS. 1, 2,
and 3. The parts and units of ion-beam source 100 similar to those
of FIGS. 1 through 3 will be designated by the same reference
numerals with an addition of 100. Thus, ion source 100 has a hollow
cylindrical housing 140 made of a magnetoconductive material such
as Armco steel which is used as a cathode. As shown in FIG. 5 by
broken lines, in the illustrated embodiment housing 140 has a
substantially rectangular top-view configuration with side walls
143a, 143b, a closed flat bottom 144 (FIG. 4) and a flat top side
146 with a closed-loop ion emitting slit 152. This slit has
predetermined shape and geometric dimensions defined by its inner
profile 152a and an outer profile 152b. It is understood that the
oval shape is shown in FIG. 5 only as an example and that the slit,
as well as the cathode, anode, and permanent magnet may be of any
required configuration such as circular, rectangular, elliptic,
etc.
A working gas supply hole 153 is formed in bottom wall 144. Flat
top side 146 functions as an accelerating electrode. Placed inside
the interior of hollow cylindrical housing 140 between bottom 144
and top side 146 is a magnetic system which includes a permanent
magnet 166 with poles N and S of opposite polarity. The N-pole
faces flat top side 146 and the S-pole faces bottom side 144 of the
ion source. The purpose of the magnetic system with a closed
magnetic circuit formed by parts 166, 146, 152, 143, and 144 is to
induce a magnetic field in ion emission slit 152. It is understood
that this magnetic system is shown only as an example and that it
can be formed in a different manner, e.g., as in aforementioned
U.S. Pat. No. 4,122,347. A closed-loop anode 154 which is connected
to a positive pole 156a of an electric power source 156 is arranged
in the interior of housing 140 around magnet 166 and concentrically
thereto. Anode 154 is fixed inside housing 140 by means of an
annular body 148 of the same top-view configuration as the anode.
Body 148 is made of nonmagnetic dielectric material such as
ceramic. Anode 154 has a central opening 155 in which a permanent
magnet 166 is installed with a gap 154a between the outer surface
of the magnet and the inner wall of opening 155. A negative pole
156b of electric power source is connected to housing 140 which is
grounded at G.sub.1.
Located above housing 140 of the ion source of FIGS. 4 is a sealed
vacuum chamber 157 which has an evacuation port 159 connected to a
source of vacuum (not shown). An object OB.sub.1 to be treated is
supported within chamber 157 above ion emitting slit 152, e.g., by
gluing it to an insulator block 161 rigidly attached to the housing
of vacuum chamber 157 by a bolt 163 but so that object OB.sub.1
remains electrically and magnetically isolated from the housing of
vacuum chamber 157. However, object OB.sub.1 is electrically
connected via a line 159 to negative pole 156b of power source 156.
Since the interior of housing 140 communicates with the interior of
vacuum chamber 157, all lines that electrically connect power
source 156 with anode 154 and object OB.sub.1 should pass into the
interior of housing 140 and vacuum chamber 157 via conventional
commercially-produced electrical feedthrough devices. In FIG. 4,
these feedthrough devices are shown schematically and designated by
reference numerals 140a and 157a. Reference numeral 157b designates
a seal for sealing connection of vacuum chamber 157 to housing
140.
An ion beam is visible in the form of a strand of light so that its
shape and position with respect to the surface of object OB.sub.1
can be observed during the operation of the ion source. To view
this, vacuum chamber 157 has a transparent sealed window W1 in one
of its walls.
To this point, the apparatus of FIG. 4 is identical to that of FIG.
1. However, an essential distinctive feature of ion-beam source 100
of FIG. 4 is that its cathode 140 has a stationary portion 146S and
moveable portions 146a and 146b which are located on opposite sides
of upper wall 146 and are guided in guides 142a and 142b rigidly
attached to or made integrally with side walls 143a and 143b of
cathode 140.
FIG. 4A shows zone D of FIG. 4 that illustrates details of slit
width adjustment mechanisms on a larger scale. Although only one
mechanism is shown, the reference numerals relate to left-hand and
right-hand mechanisms as they are identical. Cathode portions 142a
and 142b have recesses 147a and 147b that receive rods 151a, 151b.
One end of each rod 151a and 151b is rigidly connected to moveable
part 146a, 146b of cathode 140. Other ends of rods 151a, 151b pass
via the wall of vacuum chamber 157 and via feedthrough 162a, 162b
and are attached to a cross bar 164 (FIG. 5). Cross bar 164 has a
threaded opening 164a. A bolt 151 is threaded into opening 164a.
The end of bolt 151 opposite to its head 151c, which is used as a
handle, has a collar 149 which freely rotates in a recess 147 made
in the housing of vacuum chamber 157 or, as shown in FIGS. 4a and
5, is formed by a cup-shaped body 165 attached to the vacuum
chamber housing.
Feedthrough devices 162a and 162b are commercially produced units
known as manual linear feedthrough mechanisms. Such devices are
made in the form of bellows and are produced, e.g., by Huntington
Mechanical Laboratories, Inc. In the present embodiment of the
invention, bellows 162a, 162b are sealingly connected at one end to
the outer surface of the vacuum chamber housing and at the other
end to the surface of cross bar 164. Thus moveable parts 146a and
146b can be moved linearly by rotating handle 151c from the outside
of the vacuum chamber without violation of vacuum in the vacuum
chamber.
As shown in FIG. 5, inner ends 146a1, 146a2 and 146b1, 146b2 of
respective moveable portions 146a and 146b of cathode 140 have
triangular configuration in order to conform to an oval-shaped
stationary part 146S. This allows for maintaining the thickness of
ion-emitting slit 152 substantially uniform all over the perimeter
of the slit.
Unless the width of slit 152 is adjusted, the closed-loop slit has
predetermined geometric dimensions, and operation of ion source 100
is the same as that of the ion source of FIGS. 1 through 3.
Therefore the detailed operation of ion source 100 will be
omitted.
When it is necessary to adjust the width of closed-loop
ion-emitting slit 152, handle 151c is rotated in a counterclockwise
or clockwise direction, depending on whether slit 152 is to be
expanded or narrowed. As handle 151c rotates, the threaded portion
of bolt 151 engages the threaded opening of cross bar 164. Since
head 149 can rotate in recess 147 but cannot move in the direction
of the axis of bolt 151, cross bar 164 and hence rods 151a and 151b
begin to move. As rods 151a and 151b are rigidly connected to
moveable parts 146a and 146b of the cathode, the latter are
shifted, with respect to stationary part 146S of the cathode,
toward each other or in opposite direction, depending on the
direction of rotation of handle 151c.
When the width of ion-emitting slit is increased, the oval-shaped
beam IB1 is diverged and covers a larger area of the object being
treated. When the width of the ion-emitting slit is decreased, the
oval-shaped beam IB1 is converged and covers a smaller area of
object OB.sub.1. The convergence and divergence of ion beams change
its shape and thus the nature of treatment (cleaning, etching, or
coating). The apparatus of the invention allows adjustment during
the operation of the source, so that shape of ion beam IB1 and its
location with respect to object OB1 may be observed through
transparent sealed window W1.
Another feature of ion source 100 with an adjustable slit width is
that it allows to adjust an average energy of ions on the beam.
When the slit width is decreased, the ionization zone approaches
the anode surface, and the average ion energy increases.
Furthermore, ion source 100 allows adjustment of energy of
electrons and thus of the composition of the ion beam, in case of a
multiple-component gas used as a working medium. This feature
ensures selectivity of the process, e.g., in reactive ion-beam
etching.
FIGS. 6, 6A, and 6B--Ion-Beam Source with Part of Cathode Moveable
in the Beam-Propagation Direction
FIG. 6 is a sectional side view of an ion-beam source according to
another embodiment of the invention with an ion-emitting slit
configuration adjustable by shifting a moveable part of the cathode
in the direction of the beam propagation.
To some extent, the ion-beam source of this embodiment, which as a
whole is designated by reference numeral 200, is similar to ion
source 100 of the embodiment shown and described with reference to
FIGS. 4 and 5. Therefore, the parts and units of ion-beam source
200 similar to those of FIGS. 4 and 5 will be designated by the
same reference numerals with an addition of 100 to designations of
FIGS. 4 and 5. The description of identical parts will be
omitted.
In this ion beam source, a central portion 246a of a cathode 246 is
moveable together with a magnet 266 relative to the remaining
stationary portion 246b of the cathode. In the example, illustrated
in FIG. 6, ion-emitting slit 252 is formed between moveable portion
246a and stationary portion 246b of cathode 246 which, in turn,
form a housing 240 of ion source 200. In the illustrated
embodiment, surfaces of portions 246a and 246b that face object OB2
are flat and parallel to each other. Magnet 266 is rigidly attached
at its N pole, e.g., by screws (not shown), to a moveable portion
246a. Attached to S-pole side of magnet 266 is a magnetoconductive
piston portion 266b. Lower wall 244 of housing 240 has a guide
portion 244a for guiding the end of magnet 266 with piston portion
246b in the direction of propagation of a beam IB2. Movement is
carried out with the use of a mechanism similar to the one shown in
FIG. 4A. More specifically, a bolt 251 has a threaded portion 251a
engageable with a threaded opening 242 in the lower part 245 of the
housing. A head 249 of the bolt is placed in a recess 247a of a
block 247 with possibility of rotation with respect thereto. Block
247 is rigidly attached to the end of a rod 266c of piston 266b.
Rod 266c via a feedthrough 243a into lower part 245 of the housing.
The end of bolt 251 opposite to piston 266b passes outside part 245
of the housing and supports a handle 249. An anode 254 is supported
in housing 240 by a block 248 of a nonmagnetic material.
Similar to the embodiment of FIGS. 4 and 5, the apparatus of FIG. 6
has a transparent sealed window W2 in the wall of a vacuum chamber
257.
For adjusting operation conditions of ion source 200, moveable
portion 246a can be displaced to a required position with respect
to the stationary portion of housing 240, thus changing the
configuration and performance characteristics of ion-emitting slit
252. More specifically, as shown in FIGS. 6A and 6B, which
illustrate configurations of ion beam at different position of
moveable portion 246a, when the upper surface of moveable portion
246a of the cathode is below the surface of stationary portion 246b
(FIG. 6A), ion beam 252 has a converging configuration, and when
the upper plane of moveable portion 246 of the cathode is above the
plane of stationary portion 246b (FIG. 6B), ion beam 252 has a
diverging configuration.
Thus it has been shown that the present invention provides a
universal cold-cathode type ion source with closed-loop electron
drifting which allows formation of ion beams of chemically-active
substances for treating stationary objects with large surface
areas, has an extended service life, provides ion beams of high
uniformity, allows the use of a wide range of chemically-active
working media, provides an increased energy of ions produced in the
charge gap which allows treatment of distantly located objects,
provides an ion source of the aforementioned type suitable for
simultaneous treatment of objects from different sides with a
plurality of selectively controlled ion beams, and allows
adjustment of an ion beam to form ion beams of different
configurations.
Although the invention has been shown in the form of specific
embodiments, it is understood that these embodiments were given
only as examples and that any changes and modifications are
possible, provided they do not depart from the scope of the
appended claims. For example, the cathode housings of ion sources,
as well as ion emitting slits, and anodes may have configurations
other than rectangular, circular, oval, or elliptic. Moveable parts
of cathodes can be displaced with the use of different mechanisms
such as a mechanism for synchronous movement of both moveable parts
of the cathode. Anodes may be secured inside cathode housings to a
block of nonmagnetic materials by fasteners, press fits, glues,
etc. The objects to be treated may be fixed by bolts which, at the
same time, may be used for grounding the objects. Working media may
comprise different gases or their combinations. The objects to be
treated may be different in shape and dimensions and may be
subjected to different sequence of treatment. In the embodiment
with a part of the anode moveable in the direction of beam
propagation the permanent magnet is shown rigidly attached to the
moveable anode part. It is understood that the magnet may remain
stationary and the anode part may move alone.
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